Main content
High school biology - NGSS
Course: High school biology - NGSS > Unit 4
Lesson 2: Flow of energy and cycling of matter in ecosystems- Flow of energy and matter through ecosystems
- Impact of changes to trophic pyramids
- Flow of energy and cycling of matter in ecosystems
- Understand: flow of energy and cycling of matter in ecosystems
- Apply: flow of energy and cycling of matter in ecosystems
© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice
Flow of energy and cycling of matter in ecosystems
Review your understanding of the movement of energy and matter in ecosystems with this free article aligned to NGSS standards.
Key terms
| Term | Meaning |
|---|---|
| Photosynthesis | The process by which plants, algae, and other photosynthetic organisms capture energy from sunlight to create organic molecules that can be used as food |
| Cellular respiration | The process by which organic molecules from food react chemically with other compounds, releasing energy that is used for essential life processes |
| Producer | An organism that produces its own organic food molecules from inorganic sources, typically using energy from the sun |
| Consumer | An organism that obtains organic molecules by consuming other organisms as food. Primary consumers eat producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers. |
| Decomposer | An organism that obtains energy by breaking down nonliving organic matter, such as discarded plant material, the remains of dead organisms, or animal waste |
| Food web | A model that shows how matter and energy are transferred among producers, consumers, and decomposers in an ecosystem |
| Trophic level | An organism’s position relative to the primary energy source (such as the sun) in a food chain |
| Ecological pyramid | A model that represents the relative amount of matter and energy contained within each trophic level of an ecosystem |
The movement of energy and matter in ecosystems
Energy flows through an ecosystem, while matter cycles within it. To understand why this is the case let’s take a closer look at how different life processes drive the movement of energy and matter in ecosystems.
Energy enters an ecosystem when producers carry out photosynthesis, capturing energy from the sun and storing it as chemical potential energy. During this process, matter from the environment (in the form of and ) is taken in and rearranged into organic molecules (sugars). These organic molecules can power the producers’ life processes via cellular respiration (which releases and heat), or they can be stored as biomass.
Next, energy and matter move up the trophic levels of an ecosystem as producers are eaten by primary consumers, which are then eaten by secondary consumers, and so on. Some of the organic material eaten by consumers is used for cellular respiration (again, releasing and heat), some is stored as biomass, and the rest is excreted as waste.
Dead producers and consumers and their waste products provide matter and energy to decomposers. Decomposers transform matter back into inorganic forms that can be recycled within the ecosystem.
So, the energy that enters an ecosystem as sunlight eventually flows out of the ecosystem in the form of heat. In contrast, the matter in an ecosystem is continuously recycled as atoms are combined and recombined in different ways.
Energy and matter are conserved during ecosystem processes
As energy moves through an ecosystem, it changes form, but no new energy is created. Similarly, as matter cycles within an ecosystem, atoms are rearranged into various molecules, but no new matter is created. So, during all ecosystem processes, energy and matter are conserved.
Food webs model matter and energy transfer
A food web is a model of feeding relationships in an ecosystem. When an organism is eaten, the matter and energy stored in its tissues are transferred to the organism that eats it. The arrows in a food web represent this transfer.
For example, the arrow pointing from the mouse to the coyote in the food web below shows that matter and energy are transferred to coyotes when they eat mice.
Ecological pyramids model energy loss
Ecological pyramids show the relative amounts of matter or energy in different trophic levels of an ecosystem.
In most ecosystems, only about 10% of the total energy available at a given trophic level is transferred to the next level. The rest is used to power life processes, is discarded as waste, or is simply not consumed. An energy pyramid, such as the one below, illustrates this inefficiency by representing the energy available at each trophic level with a differently sized tier.
A consequence of the inefficient energy transfer between trophic levels is that there tends to be fewer organisms at higher trophic levels in an ecosystem. The number of organisms at different trophic levels can be represented by a numbers pyramid, such as the one shown below.
What else should I know about trophic levels and food webs?
- Organisms can occupy more than one trophic level. Organisms are not limited to one trophic level. For example, omnivores (which eat plants and animals) can be classified as primary or secondary consumers.
Want to join the conversation?
this makes so much sense(10 votes)
I still don't understand this food web so can somebody hear explain it to me(2 votes)
so the food web consists of producers which are plants like grass which then get eaten by primary consumers like a mouse then there is a heterotrophic animal such as a snake that eats the mouse and the at the top of the food web there is an apex predator that eats the stuff in the food web but doesn't get eaten by anything in the food web such as a hawk. And while the animals are eating each other only roughly 10 percent of the energy goes to the next animal because there is more of that animal in the ecosystem to an example would be the mouse eating the grass the mouse would get about 10 percent of the energy because there is way more grass out in the ecosystem(11 votes)
- Where would we be on the food chain and web(3 votes)
The very very top because we, the humans of this world, kill everything(9 votes)
- so the food web consists of producers which are plants like grass which then get eaten by primary consumers like a mouse then there is a heterotrophic animal such as a snake that eats the mouse and the at the top of the food web there is an apex predator that eats the stuff in the food web but doesn't get eaten by anything in the food web such as a hawk. And while the animals are eating each other only roughly 10 percent of the energy goes to the next animal because there is more of that animal in the ecosystem to an example would be the mouse eating the grass the mouse would get about 10 percent of the energy because there is way more grass out in the ecosystem(5 votes)
this makes a lot of sense(4 votes)
tertiary consumers count as vultures (vultures are decomposers) therefore, decomposers are tertiary consumers(3 votes)
Some tertiary consumers are decomposers.(2 votes)
where does the excess heat that spills of the organisms go and does that then somehow get recycled back into the ecosystem if so how?(1 vote)- Heat in general does not get recycle, but some heat warms the earth, and some heat goes back into space. I believe that heat can also create some air/water currents (which later get lost as heat again). To maintain the earth's average temperature constant, the earth should send the same amount of radiation (heat) into space as it receives from the sun (although at a different frequency).(1 vote)
- Can the number for the numbers pyramide at the end of the article be correct, even as an estimate? 9000 mice for 1000m² (0.1 ha, roughly the size of a house with a garden) sounds a lot for such a small area to sustain?(0 votes)
- what is photosynthesis,potential,and continuously(0 votes)
Photosynthesis is not an event but rather a process. It occurs continuously whenever sunlight is present. As soon as the sun rises, photosynthesis begins. Energy from sunlight drives the process and so will continue as long as sunlight is available(1 vote)
COuld you give a better explanation?(0 votes)
